(1) Field of the Invention
The present invention relates to a flame-retardant olefin polymer composition excellent in heat resistance and mechanical strength which is composed basically of an ethylene-.alpha.-olefin copolymer having a density of 0.86 to 0.91 g/cm.sup.3, a boiling n-hexane insoluble matter of 10% by weight or more and a maximum peak temperature of 100.degree. C. or more in terms of differential scanning calorie meter and an olefin polymer modified with an unsaturated carboxylic acid or its derivative, and an electrical material using the above mentioned composition.
(2) Description of the Prior Art
A polyethylene is excellent in physical and chemical properties and thus is often utilized in many fields as household and industrial aritcles which are molded into films, sheets, pipes, containers and the like by various molding methods such as extrusion, injection molding and rotary molding.
The polyethylene is easily combustible, and accordingly methods for rendering it flame-retardant have heretofore been suggested.
The most general method of these suggestions intends to obtain flame-reatardant properties by adding a flame retarder containing a halogen or phosphorus to the polyethylene. The degree of its flame retardance is heightened along with the increase in an amount of the flame retarder to be added. However, it is known that the increase in the amount of the flame retarder brings about the deterioration in mechanical strength and workability and additionally impairs flexibility and low-temperature resistance disadvantageously. Further, from the viewpoint of fire prevention, it is required that the flame-retardant composition has higher flame retardance, and such a requirement is imposed as duty in some districts as a recent tendency. The above mentioned requirement can be satisfied with non-environmental pollution type inorganic flame retarders such as magnesium hydroxide and aluminum hydoxide which will not generate a harmful gas and will emit a less flame in the time of combustion, and their demand is rapidly getting larger (these techniques are described in, for example, Japanese Patent Provisional Publication Nos. 132254/1976, 136862/1981 and 13832/1985).
However, the polyethylene which is now commercially available is particularly poor in the acceptance of the inorganic flame retarder, so that its flame-retardant effect is low. Such a type of polyethylene additionally has the drawback that when a content of the inorganic flame retarder is heightened, mechnical strength, flexibility and workabilty will deteriorate, so that it will be impracticable. On the other hand, for the purpose of heightening the content of the inorganic flame retarder, a technique of using a flexible resin such as an ethylene-vinyl acetate copolymer, an ethylene-ethyl acrylate copolymer, a chlorinated polyethylene or an ethylene-propylene copolymer rubber is well known. However, such a technique is poor in mechanical strength such as tensile strength and heat resistance.